With the remarkable progress of Internet technologies and the rapid development of Internet services, the needs of establishing a network connection by using an instant messenger (IM) tool and transferring a file directly from one terminal to another terminal become increasingly popular.
FIG. 1 is a schematic diagram of an existing file transfer system. As shown in FIG. 1, the file transfer system includes a file sending terminal 11 and a file receiving terminal 12, both being connected to a network 13. The file sending terminal 11 may request, by using a handshake protocol, to establish a persistent connection to the file receiving terminal 12. The file sending terminal 11 may continuously read content of a file to be transferred, and then after the persistent connection is established successfully, send the read content of the file to the file receiving terminal 12 over the persistent connection. The file receiving terminal 12 creates a file and continuously writes the received content of the file in the created file. The entire process is repeated over and over again till the entire process of file transfer is completed. The persistent connection refers to one network connection over which multiple data packets can be continuously sent and in which both parties need to send a link detection packet if no data packet is sent while the connection is kept.
However, in current network access technologies, an asymmetric digital transmission technology, for example, an Asymmetric Digital Subscriber Line (ADSL) or a similar network technology is generally used. Such a technology is characterized in that an uplink bandwidth and a downlink bandwidth are asymmetric. On a network connection based on an asymmetric digital transmission technology, an uplink maximum transfer rate is much lower than a downlink maximum transfer rate. For example, on generally involved 1 M, 2 M, and 10 M ADSL broadband network connections, these 1 M, 2 M, and 10 M bandwidths are all downlink bandwidths. A maximum download speed of the 1 M bandwidth is about 128 kb/s, and a maximum download speed of the 2 M bandwidth is about 256 kb/s. However, a maximum upload speed of the 1 M bandwidth is 64 kb/s, and hardly exceeds 50 kb/s on an actual network connection. A transfer process of the file transfer system in FIG. 1 is used as an example, in which a file to be transferred by the file sending terminal is 1.0 GB, a network uplink rate of the file sending terminal is 50 kb/s, and a network downlink speed of the file receiving terminal is 256 kb/s. If the entire network of the file sending terminal is occupied to transfer the file, time to be consumed by the entire transfer process is about 349 minutes, which is mainly restricted by the uplink speed of the file sending terminal. Therefore, in an existing process of file transfer, an uplink transfer rate of a file sending terminal becomes a bottleneck of file transfer, causing that a current file transfer speed is restricted by an uplink bandwidth of a terminal, and the transfer speed is low.